The notion of counting years has been around for as long as we, human, have written records, but the idea of syncing up where everyone starts counting is relatively new. The widely standard calendar we use today is to designate years based on a traditional reckoning of the year when a person called Jesus Christ was born, and that is the A.D. and B.C. system (which also explained the standard calendar is also called “Christian calendar”).
The abbreviation A.D. stands for Anno Domini which comes from Latin words for “in the year of the Lord.” It refers particularly to the birth of Jesus Christ. There is also another abbreviation called B.C. which stands for “Before Christ.” In English, it is common for A.D. to precede the year, so that the translation of A.D. 2020 would read “in the year of our Lord 2014.” In recent years, however, an alternative form of A.D. and B.C. has gained resistance. Many publications both of academics and of non- academics adopt the abbreviation B.C.E. for “Before Common Era and C.E. for “Common Era.” But Before we discuss further with how and why the system was invented, let us take a look at the historical background that linked A.D and B.C. system with Jesus’ birth.
In the early Middle Ages, the most important calculation, and hence one of the main motivations for the European study of mathematics, was the problem of when to celebrate Easter. The First Council of Nicaea in A.D. 325, had decided that Easter would fall on the Sunday following the full moon that follows the spring equinox (see https://www.britannica.com/event/First-Council-of-Nicaea-325). The computation was the procedure for calculating this most important date, and the computations were set forth in documents known as Easter tables. It was on one such table that, in A.D. 525, Roman scholar and theologian Dionysius Exiguus of Scythia Minor introduced the A.D. system (see https://www.encyclopedia.com/people/history/historians-european-biographies/dionysius-exiguus). The purpose is to count the years since the birth of Jesus Christ.
Dionysius devised his system to replace the Diocletian system, named after the 51st emperor of Rome, who ruled from A.D. 284 to A.D. 305. The first year in Dionysius’ Easter table, “Anno Domini 532,” followed the year “Anno Diocletiani 247.” He then made the change specifically to do away with the memory of this emperor who had been a brutal persecutor of Christians.
Dionysius, nevertheless, never explained how he determined the date of Jesus’ birth, but some scholars theorise that he used current beliefs about cosmology, planetary conjunctions, and the precession of equinoxes to calculate the date. He attempted to set A.D. 1 as the year of Jesus’ birth, but was off in his estimation by a few years, which is why the best modern estimates place Jesus’ birth at 4 B.C.
Meanwhile, the addition of the B.C. component itself took place two centuries after Dionysius, when the Saint Bede (also known as Venerable Bede) of Northumbria published his “Ecclesiastical History of the English People” in 731. Up until this point, Dionysius’ system had been widely used. Bede’s work not only brought the A.D. system to the attention of other scholars, but also expanded the system to include years before A.D. 1. Prior years were numbered to count backward to indicate the number of years an event had occurred “before Christ” or B.C.
Journalist and author Charles Seife in his book “Zero: The Biography of a Dangerous Idea” (2000) notes: “To Bede, also ignorant of the number zero, the year that came before 1 A.D. [sic] was 1 B.C. There was no year zero. After all, to Bede, zero didn’t exist.” In contrast to Bede’s who did not recognise the existence of zero, the number did exist.
Zero, as we know today, was first published in A.D. 628 by Indian scholar Brahmagupta (see https://www.storyofmathematics.com/indian_brahmagupta.html). But, the notion would not spread to medieval Christian Europe until the eleventh to thirteenth centuries.
The B.C. and A.D. system just gained its popularity after the Roman Emperor Charlemagne adopted the system for dating acts of his government throughout Europe in the ninth century (compare with https://www.britannica.com/biography/Charlemagne/Religious-reform). And by the fifteenth century, all of Western Europe had adopted the B.C. and A.D. system. The system’s inclusion was implicit in the sixteenth century introduction of the Gregorian calendar, and it later would become an international standard in 1988 when the International Organization for Standardization released ISO 8601, which describes an internationally accepted way to represent dates and times (see https://www.iso.org/standard/40874.html).
How about the use of B.C.E. and C.E in some recent publications? What was the origin? The form of “Before the Common Era” and “Common Era” dates back to 1715, where it is used in an astronomy book interchangeably with “Vulgar Era.” At the time, vulgar meant “ordinary,” rather than “crude.” We could find the term “Vulgar Era” in the writings of astronomer and mathematician Johannes Kepler (see https://www.ancient.eu/article/1041/the-origin-and-history-of-the-bcece-dating-system/).
So there are, at least, two reasons for the transition from B.C. to B.C.E. and A.D. to C.E. First, it shows a sensitivity to those who use the same year number as that which originated with Christians, but who are not themselves Christian. Second, the label “Anno Domini” is arguably inaccurate, since scholars generally believe that the person called Jesus Christ was born some years before A.D. 1, and that the historical evidence is no adequate enough to allow for definitive dating.
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